This invention relates generally to space conditioning systems for conditioning the temperature and humidity of air supplied to an enclosed space and in particular to a space conditioning system having multiple stages of cooling and dehumidification capability.
Space conditioning systems, including systems which use a vapor compression refrigerant to cool air recirculated to a conditioned space, often require relatively accurate control of the humidity in the air within the conditioned space. In one such system, as described in U.S. Pat. No. 5,622,057, a heat exchanger is positioned downstream of the system evaporator to subcool the condensed liquid refrigerant before it enters the evaporator, to enhance dehumidification of the air passing through the evaporator and to reheat the air after it passes through the evaporator. A major disadvantage of this type of system is that dehumidification of the air supplied to an indoor space occurs only when there is a cooling demand. Another disadvantage of prior art space conditioning systems using vapor compression is that more energy input is required to provide the required cooling, dehumidification and reheat of the circulated air because the air must be cooled below the temperature required to meet the cooling demand in the space in order to dehumidify the air and then the air must be reheated to a desired temperature.
An improved space conditioning system which provides dehumidification of air supplied to an enclosed space is described in co-pending U.S. Pat. No. 6,427,461. In this system, dehumidification is provided by cooling and reheating air supplied to the space in the absence of a demand for cooling when there is a demand for dehumidification. However, if a cooling demand occurs at the same time as a demand for dehumidification, priority is given to meeting the cooling demand, regardless of the dehumidification requirements.
Accordingly, there is a need for an improved space conditioning system having the capability to simultaneously meet both a cooling demand and a dehumidification demand.
In accordance with the present invention, a space conditioning system for conditioning air within an enclosed space is comprised of an air mover for circulating air to the enclosed space; plural discrete refrigeration circuits, each of which is operable in a cooling mode wherein air circulated to the space is cooled and at least one of which is further operable in a reheat mode wherein air circulated to the space is first cooled and then reheated; and a controller for selectively controlling the system to provide the space with conditioned air.
In accordance with an aspect of the invention, the controller is operable to cause at least one of the refrigeration circuits to operate in the cooling mode in response to a demand for cooling in the space and at least another one of the refrigeration circuits to operate in the reheat mode in response to a demand for cooling and a demand for dehumidification in the space both being present.
In accordance with another aspect of the invention, the controller is operable to prevent any of the refrigeration circuits from operating in the reheat mode in response to a predetermined level of cooling demand in the space (e.g., a second stage or higher demand), even if a demand for dehumidification is also present. Therefore, in response to a higher level of cooling demand, priority is given to satisfying the cooling demand over the dehumidification demand.
Still further, the invention provides a space conditioning system having a damper for admitting ambient outdoor air to the system for circulation to the enclosed space and an enthalpy sensor for sensing the enthalpy of the outdoor air. The controller is further operable to control the damper to allow the outdoor air to be admitted to the system in response to a demand for cooling in the space when the enthalpy of the outdoor ambient air satisfies a predetermined condition. In accordance with yet another aspect of the invention, the controller is operable to inhibit the outdoor ambient air from being admitted to the system when a demand for dehumidification is present, even when a demand for cooling is also present and the enthalpy of the outdoor ambient air satisfies the predetermined condition.
In accordance with a preferred embodiment of the invention, the system includes four discrete refrigeration circuits, all of which are operable in the cooling mode and at least two of which are also operable in the reheat mode. Each circuit includes a condenser for condensing the vapor refrigerant, an evaporator for evaporating the liquid refrigerant and a compressor for compressing the vapor refrigerant and for circulating the refrigerant through the circuit. Each of the refrigeration circuits operable in the reheat mode further includes a reheat heat exchanger downstream of the evaporator for heating air cooled by the evaporator to a temperature above the temperature of air discharged from the evaporator when the circuit is operated in the reheat mode. The air is cooled and dehumidified by the evaporator and then reheated by the reheat heat exchanger so that dehumidified (but not substantially cooled) air is provided to the space in response to a demand for dehumidification of the air therein.
In accordance with the present invention, a space conditioning system is provided having the capability of simultaneously satisfying both a demand for cooling and a demand for dehumidification in an enclosed space, with priority given to satisfying the cooling demand. This is accomplished by operating at least one of the refrigeration circuits in the cooling mode and at least one of the refrigeration circuits in the reheat mode, as described hereinabove. Nevertheless, in response to a higher level of cooling demand, the cooling demand takes priority and all of the refrigeration circuits are inhibited from operating in the reheat mode until the higher level cooling demand is satisfied.